1. Field of the Invention
This invention relates to a method and composition for preventing and/or reversing sensorineural hearing loss (SNHL) or toxin-induced hearing loss. More specifically, this invention relates to the use of agents which augment inner ear antioxidant defenses such as adenosine agonists or up-regulating agents and/or agents which increase inner ear glutathione levels to prevent and/or reverse hearing loss induced by noise or toxin. In addition, this invention covers agents that curtail activated programmed cell death pathways and induce/enhance cell repair mechanisms in the inner ear.
2. Description of the Prior Art
SNHL is a very common problem for service members and civilian government employees. Approximately 450 million dollars is spent annually to compensate service members for hearing loss (1). Despite hearing conservation programs, 20-30% of service members develop compensable hearing loss after 10 years in the service (2). The sense of hearing is critical for combat and operational readiness of soldiers and sailors. Both temporary and permanent hearing threshold impairments decrease the ability to communicate and to detect enemy movements (3). Successful implementation of medical treatment to prevent or reverse SNHL as an augmentation to established hearing conservation programs has the potential to save millions of dollars annually and to significantly improve operational readiness.
It is established by the Center for Disease Control that approximately 30 million people in the U.S. suffer from SNHL (4). The potential for commercialization is very extensive and would include workers in factories, construction operations, communications, and the airline industry to name a few. Many people working in an environment with damaging noise or toxins would potentially benefit from this treatment. In addition, individuals receiving toxic medications for other forms of therapy (i.e. cancer chemotherapy) can suffer SNHL. An idiopathic form of SNHL also exists.
Currently there are no published effective topical medications to prevent or reverse SNHL. There are no published reports of topical, oral, or systemic medications to treat noise-induced hearing loss (NIHL). This invention differs from mechanical noise attenuators or hearing protection devices in that it does not need to be worn and does not decrease hearing acuity as hearing protectors do. Also, this treatment has the potential to reverse SNHL after it is occurred.
Additionally, cisplatin and aminoglycoside antibiotics such as gentamicin represent useful commonly prescribed therapeutic agents which are toxic to the ear and cause sensorineural hearing loss (6,7,15). Gentamicin is used as an agent delivered indirectly to the inner ear via the middle crossing the round window membrane to destroy balance function in an inner ear affected by Meniere's disease (28). One of the limitations of this therapy is that the auditory portion of the inner ear is also often damaged leading to sensorineural hearing loss (29). Thus there is a need to selectively protect the auditory hair cells while eliminating inner ear balance function with the gentamicin.